Vehicle mass is a parameter of interest particularly in the area of road freight. There are different elements which make up vehicle mass:                the mass of the vehicle and trailer itself which are together referred to as vehicle tare;        the mass of the load applied to the vehicle which is referred to as the payload; and        the total mass of the vehicle and its load which are together known as the total combination mass (TCM).        
Vehicle tare may vary due to fuel loads but for the most part, this has little impact on the mass of a loaded vehicle during its journey. Commercial payload is typically measured at the point of loading and is usually an important figure in a commercial transaction. If the mass is not known or cannot be determined during the loading process, then weighbridges are used at the unloading site or elsewhere; the tare is deducted from the TCM measured by the weighbridge to determine payload.
Vehicle mass monitoring requirements depend on the needs of the end user of the mass data. For obvious reasons, customers, transporters and suppliers are interested in payload mass as this bears directly on financial return. Road authorities are likely to be more concerned about the overall TCM and axle group mass during travel as this can lead to assumptions about the impacts that use of that vehicle will have on traffic and the road pavement and bridges.
Static vehicle mass measurements used by transporters and suppliers are commonly determined using weigh-in-motion (WIM) stations, weighbridges (static and low speed) and portable scales. Once mass data is obtained using one of these systems, it may be recorded by the driver into vehicle log books. This is a static mass data entry, i.e. a snapshot of vehicle mass at that time. WIM stations enable a vehicle to be weighed without stopping. WIM data is low cost to collect but is inadequate for use in an evidentiary monitoring system because it is less precise. Weighbridges are more accurate but labour intensive and therefore higher cost. Another deficiency of currently used vehicle weighing techniques is that they only provide for intermittent checking of vehicle mass, e.g. when the vehicle is in the vicinity of a WIM station or weighbridge. Typically both weighbridges and WIM stations are permanent sites provided in main vehicle corridors which may not meet the needs of all users.
On-board mass-monitoring (OBM) is another means to measure mass and is capable of continuously monitoring mass for a vehicle during the course of its journey which may include intermittent loading and unloading points. An OBM sensor is essentially some form of transducer incorporated into the vehicle's suspension system to measure the mass of an individual axle or an entire axle group. For steel sprung suspensions, this typically involves use of load cells containing strain gauges. These are also used for the turntable of prime movers (fifth wheel). Load cells are usually installed as an integral part of the vehicle or trailer structure, as a load bearing member. For air bag suspensions, an OBM device typically involves use of air pressure transducers connected to the air output lines from the airbags of the vehicle suspension system.
In some OBM systems the electrical signal from the mass transducer is fed into some form of electronic buffer (typically associated with an axle group or vehicle combination unit). The buffer may condition or pre-process the incoming signal, combine/collate a number of incoming signals, digitise an incoming analogue signal by sampling at a particular frequency (e.g. 100 Hz to 20,000 Hz), store a number of mass records or even convert the mass signal to an actual mass value based on some pre-defined formula. Most OBM devices (also known as on-board vehicle mass-monitoring systems or OVMS) also provide some form of interface that allows users to configure the system, read and extract mass data from the unit and connect to other devices such as printers and wireless communications devices. In some systems this component also performs the functions of electronic buffers.
The commercial investment in an OBM system fitted to a vehicle can be justified in many cases because it permits the driver during loading to more accurately distribute the mass of the load on the vehicle (i.e. to legal weight limits over each axle group) and to reduce instances of under-loading which leads to revenue loss. Also, monitoring vehicle mass and load distribution using OBM devices reduces instances of overloading which can lead to lost profits due to fines (and loss of travel time), missed delivery deadlines and increased risk of hazard and accidents as well as uneven wear on vehicle tyres and the like.
There are various possibilities for tampering with OBM systems. For example, exposed cables in air bag suspension systems and the ability to “chock” load cell transducers on turntables expose OBM systems to tampering. Electronic tampering is less likely since most systems are password protected but this cannot be ruled out. Research indicates there is little incentive to tamper with OBM systems since the drivers themselves benefit from using them. Nevertheless, tamper-evidence is crucial to utilise measurements from OBM devices in an evidentiary system whose data can be relied on to check compliance with regulatory requirements.
Although a range of mass-monitoring devices are available on the market, few of them have the capability to provide mass determinations which can be used at an evidentiary level. It would be desirable to improve upon existing mass monitoring systems by providing an approach to vehicle mass monitoring which is sensitive to possible tamper attempts so that the mass data obtained can be used reliably, e.g. as evidence of vehicle compliance (or non-compliance) with mass-related conditions of vehicle use. It may also be desirable to develop an approach for providing mass quality data to indicate the health of static and/or dynamic mass data pertaining to a vehicle or axle group of the vehicle.
The discussion of the background to the invention included herein including reference to documents, acts, materials, devices, articles and the like is intended to explain the context of the present invention. This is not to be taken as an admission or a suggestion that any of the material referred to was published, known or part of the common general knowledge as at the priority date of any of the claims.